The present invention relates to a highly densifiable wood pulp product and methods for its formation and use and, more particularly, to a pulp product that includes fibers having low coarseness.
Wood pulp and paper products are conventionally formed from mature wood fiber obtained from mature tree trunks. Mature wood is characterized as having relatively high specific gravity, long and coarse fibers, high cellulose content, and thick cell walls. Mature wood is obtained from the tree trunk or body exclusive of branches and treetops. While mature trees are predominantly composed of mature wood, mature trees also include juvenile wood. Juvenile wood occurs in a zone near the pith at the heart of the tree, extending to the top of the tree, and is present in the first six to eight annual rings from the pith. Wood near the treetop is predominantly juvenile wood.
Because of its generally undesirable characteristics for some products, including low specific gravity, short fibers, low cellulose content, and thin cell walls, juvenile wood is used primarily in pulp and papermaking processes that benefit from its properties. For example, because of the collapsibility of its fibers and improved bonding properties, juvenile wood is used to make some linerboards. Additionally, some juvenile wood is used to make certain printing papers to impart smoothness to the sheet""s surface. However, most juvenile wood in the form of treetops, thinnings, and branches is generally discarded at the site of timber harvest in favor of mature wood.
Certain consumer products that include wood pulp fibers require the pulp fiber to be highly compressible and densified, while at the same time maintaining fiber matrix softness. Frequently, these properties are achieved only by the addition of relatively expensive chemical additives, for example, chemicals that disrupt intrafiber hydrogen bonding to reduce fiber stiffness and chemicals that reduce interfiber bonding to reduce web stiffness. The addition of large quantities of chemicals to wood pulp is economically disadvantageous.
Accordingly, a need exists for wood pulp products that can be highly compressed and densified while maintaining fiber softness with minimal addition of expensive chemicals. A need also exists for optimizing and efficiently utilizing forest resources including previously underutilized forest products. The present invention seeks to fulfill these needs and provides further related advantages.
In one aspect, the present invention provides a densifiable wood pulp product. In one embodiment, the densifiable product is a compressible fibrous composition that includes fibers having low coarseness, preferably having a fiber coarseness less than about 22 mg/100 m, and a densifying agent. In another embodiment, the densifiable product further includes fibers having coarseness greater than about 22 mg/100 m. Juvenile wood fibers are the preferred source of the fibers having low coarseness.
In another aspect, the invention provides a densified pulp product formed by compacting a fibrous composition that includes fibers having a fiber coarseness less than about 22 mg/100 m, a densifying agent, and optionally, fibers having coarseness greater than about 22 mg/100 m.
The products of the invention can be advantageously incorporated into absorbent articles such as diapers, feminine care products, and adult incontinence products. Thus, in further aspect, the invention provides absorbent articles that incorporate the fibrous products of the invention. In these applications, the products can optionally include absorbent material such as superabsorbent polymeric material.
Methods for forming the densifiable and densified fibrous products of the invention are also provided.